Dust Suppression and Reduction of Surface Oxidation for Mineral Agglomerates

ABSTRACT

The present invention provides a composition consisting essentially of a mineral substrate and a dust suppresant, which is adhered to the surface of the mineral substrate, and methods of reducing dust generation of a mineral substrate by applying a dust suppresant to the surface of the mineral substrate. The dust suppresant is a natural or synthetic triglyceride.

The present invention relates to a composition consisting essentially of a mineral substrate and a dust suppressant, which is adhered to the surface of the mineral substrate, and to methods of reducing dust generation of a mineral substrate by applying a dust suppressant to the surface of the mineral substrate.

WO 03/052149 A1 describes iron ore pellets having incorporated saturated hydrocarbons such as paraffin oils or synthetic oils in order to make the iron ore pellets resistant to abrasion, sticking, degradation and emission of dust. The saturated hydrocarbons are incorporated into the iron ore pellet at 250° C.

WO 2004/099452 A1 describes iron ore pellets, wherein the surface layer of the pellets is coated with polymer or synthetic oils. The amount of polymer or synthetic oil is 0.14 to 1% by weight per weight pellet. The polymer or oil is applied to the pellets at 250 to 300° C. The addition of the polymer or oil is best accomplished through the preparation of the polymer or oil diluted in 50 to 80% water.

The disadvantages of dust suppressants described in WO 03/052149 A1 and WO 2004/099452 A1 are they are saturated hydrocarbons or synthetic oils that are not very convenient to work with. They can be toxic and flammable and thus represent a health risk and they are usually not biodegradable and thus can cause environmental problems when spilt or lost due to wind carry.

Therefore, it is an object of this invention to provide a composition consisting essentially of a mineral substrate and a dust suppressant, which is adhered to the surface of the mineral substrate, wherein the dust suppressant is biodegradable and does not constitute a health risk.

This object is solved by the composition according to claim 1 and the method according to claim 7.

The dust suppressant of WO 2004/099452 A1 has the additional disadvantage that it is applied to the iron ore pellets as a preparation diluted in 50 to 80% water. This aqueous dust suppressant preparation causes spitting problems when applied to the hot iron ore pellets as it instantaneously boils.

Therefore, it is a further object of this invention to provide a more convenient method of applying dust suppressants.

This object is solved by the method according to claim 9.

The composition of the present invention consists essentially of a mineral substrate and a dust suppressant, which is adhered to the surface of the mineral substrate, wherein the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides.

Triglycerides are esters of glycerine and fatty acids. In a preferred embodiment the triglycerides are natural such as soybean oil, sunflower oil, coconut oil, palmitic oil, cottonseed oil, castor oil etc. Further triglycerides are described e.g. in Römpp Lexikon Chemie, 10^(th) edition, p. 1320 f., Georg Thieme Verlag. In a particular preferred embodiment the triglyceride is selected from the group consisting of soyabean oil, sunflower oil, coconut oil, palmitic oil, cottonseed oil, and castor oil and mixtures thereof.

The inventive method can be applied to all mineral substrates, which can be a source of dust. In particular, all known ore pellets can be used, preferably iron-ore pellets are used.

The amount of dust suppressant usually can be chosen in the range of from 0.05 to 2.5% by weight per weight of the mineral substrate. Preferably it is chosen in the range of from 0.1 to 1.5% by weight per weight of the mineral substrate.

The dust suppressant can be adhered to at least 50% of the surface of the mineral substrate. Preferably it is adhered to at least 80% of the surface of the mineral substrate and more preferably to at least 90%.

The first method of the present invention of reducing dust generation of mineral substrates comprises applying a dust suppressant to the surface of a mineral substrate having a temperature in the range of from 150 to 250° C. in an amount in the range of 0.05 to 2.5% by weight per weight of mineral substrate, wherein the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides.

Preferably, the mineral substrate is an ore pellet, preferably an iron-ore pellet.

Generally, the dust suppressant is of ambient temperature when applied to the hot pellets, but, if desired, the dust suppressant may also be of a temperature as high as the temperature of the hot pellets.

The dust suppressant may be applied by well-known methods in the art such as spraying or dipping etc., spraying being preferred.

The process can be carried out batch-wise or continuously, e.g. using a conveyor belt on which the mineral substrates or pellets are sprayed and then further cooled down or transported to its storage site.

Usually the thus treated pellets are cooled down to ambient temperature and then can be stored, transported or further treated as desired.

Also part of the invention is the use of triglycerides as dust suppressants.

The second method of the present invention of reducing dust generation of mineral substrates comprises applying a dust suppressant to the surface of a mineral substrate having a temperature in the range of from 100 to 250° C. in an amount in the range of 0.05 to 2.5% by weight per weight of mineral substrate, wherein the dust suppressant is applied in the form of a nonaqueous foam.

The dust suppressant can be a liquid nonvolatile hydrocarbon, a nonvolatile polyol, a synthetic oil or a natural or synthetic triglyceride or mixtures comprising liquid nonvolatile hydrocarbons, nonvolatile polyol, synthetic oils or triglycerides. Examples of liquid nonvolatile hydrocarbons are petroleum oil and petroleum oil products such as mineral oil. Examples of mineral oils are fuel oils, e.g. gasoline, diesel fuel, heating oil and kerosene, and lubricating oils. Examples of nonvolatile polyols are glycol and polyethyleneglycol. An example of a synthetic oil is silica oil.

Preferably, the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides. More preferably, the dust suppressant is a natural triglyceride or a mixture comprising a natural triglyceride. Examples of natural triglycerides are given above. Most preferably, the dust suppressant is selected from the group consisting of soyabean oil, sunflower oil, coconut oil, palmitic oil, cottonseed oil and castor oil or mixtures thereof.

Preferably, the mineral substrate has a temperature in the range of from 150 to 250° C.

The dust suppressant is preferably applied in the presence of a surfactant. Examples of suitables surfactants are HCF-740, which is a mixture of fluorosurfactants and hydrocarbon solvent, HCF-730, which is a nonionic mixture of silane surfactants, HCF-720, which is a nonionic mixtuture of silane surfactants and fluorosurfactants and HCF-710, which is a nonionic mixture of silane surfactants and sulfonic acids, all sold by Clearwater.

The surfactant can be used in amounts of 0.2 to 5% by weight per weight of dust suppressant. Preferably, it is used in amounts of 0.5 to 2.5% w/w and more preferably in amounts of 1 to 2% w/w.

The dust suppressant nonaqueous foam can be applied to the mineral substrate by dipping the mineral substrate onto the surface of the foam or by passing it through the foam, which can be either a static or moving mass. Alternatively, the foam can be applied to a moving mass of mineral substrate, e.g. at a transfer point on a conveyor belt.

Generally, the dust suppressant nonaqueous foam is of ambient temperature when applied to the hot pellets, but, if desired, the dust suppressant may also be of a temperature as high as the temperature of the hot pellets.

Preferably, the mineral substrate is an ore pellet, preferably an iron-ore pellet.

Also part of the invention are dust suppressants in the form of a nonaqueous oil. Dust suppressant is as defined for the second method of reducing dust generation of mineral substrates.

The dust suppressant nonaqueous foam of the present invention has the advantage that it does not cause spitting when applied to hot mineral substrates. In addition, it avoids the enhalation risks connected with spraying a dust suppressant and also allows an enhanced control of the amount of adhered dust suppressant and a better distribution of the dust suppressant on the pellets, when very low amounts of adhered dust suppressant are desired.

EXAMPLES Example 1

1.1. Preparation of a composition of iron ore pellets and soyabean oil using sprayed oil 40 plant-fired spherical iron ore pellets, (diameter from 10 to 14 mm; total weight 133.92 g) are heated to 200° C. for 1 hour (in order to simulate the temperature after leaving the furnace). The hot pellets are transferred to a wire basket and sprayed with soyabean oil, which is at ambient temperature, six times, the total amount of sprayed oil being 1.59 g or 1.19% by weight per total weight of the pellets. The contents of the wire basket are then gently agitated, by hand, for a few seconds to increase transfer of the oil from surface to surface. Thereafter the pellets are further cooled down to ambient temperature without further agitation.

1.2. Dust Measurement

35 of the thus treated pellets are then selected, weighed (111.94 g) and afterwards transferred to a sealable metal tube (6.5 cm diameter by 17.5 cm length). In order to simulate handling of the pellets the tube and its contents are then tumbled, end-to-end, in a Roaches “Dye Bath” for 2 hours at ambient temperature. Thereafter, the contents of the tube are transferred on a 500 μm sieve, where the fine material is separated from the remaining pellets. The final weight of these 35 pellets is 110.41 g, and the fine material (<500 in), is 1.53 g or (1.53/111.94)×100=1.37% by weight per weight of the untumbled pellets.

1.3. Pellet Surface Observation

A colour change from grey (plant fired pellet) to red (rustic) is an indication of surface oxidation. This change is quantifiable from a visual perspective (% surface coverage). The treatments noted here infer that surface oxidation is reduced when soyabean oil is used instead of water.

Example 2

2.1. Preparation of a composition of iron ore pellets and sunflower oil using sprayed oil Example 1.1 is repeated, except that sunflower oil is used instead of soybean oil, the number of pellets is 35, the total weight of the pellets is 130.79 g and the amount of oil is 0.21% by weight per weight of pellets.

2.2. Dust Measurement

Example 1.2. is repeated. The total weight of fine material is 0.98% by weight per weight of the untumbled pellets.

2.3. Pellet Surface Observation

A colour change from grey (plant fired pellet) to red (rustic) is an indication of surface oxidation also infer that surface oxidation is reduced when sunflower oil is used instead of water.

Comparative Example 1

Example 1 is repeated, however the 35 pellets employed (total weight 129.70 g) are not treated with a dust suppressant. The percentage of fine material is 5.56% by weight per weight of untumbled pellets.

Example 3

3.1. Preparation of a composition of iron ore pellets and soybean oil using foamed oil Nitrogen is bubbled in a mixture of 100 mL soyabean oil and 2 mL HCF-740, a mixture of fluorosurfactants and hydrocarbon solvent, which is sold by Clearwater in order to generate a stable foam. 35 plant fired spherical iron ore pellets (6.5 cm diameter by 17.5 cm length) are heated to 200° C. for 1 hour (in order to simulate the temperature after leaving the furnace). The hot pellets are transferred to a wire basket and dipped onto the surface of the foamed oil, which has ambient temperature. The total amount of oil being adhered to the pellets is measured and the percentage (weight adhered oil/weight pellets)×100 is calculated. The contents of the wire basket are then gently agitated, by hand, for a few seconds to increase transfer of the oil from surface to surface. Thereafter the pellets are further cooled down to ambient temperature without further agitation.

3.2. Dust Measurement

The thus treated pellets are weighed and transferred to a sealable metal tube (6.5 cm diameter by 17.5 cm length). In order to simulate handling of the pellets the tube and its contents are then tumbled, end-to-end, in a Roaches “Dye Bath” for 2 hours at ambient temperature. Thereafter, the contents of the tube are transferred on a 4 mm sieve, where the fine material (<4 mm) is separated from the remaining pellets. The weight of the fine material is measured and the percentage (weight fine material/weight untumbled pellets)×100 is calculated.

Example 4

Preparation of a composition of iron ore pellets and paraffin oil using foamed oil Example 3 is repeated except that SN 150, a paraffin oil, is used instead of soyabean oil, and 1 mL HCF-740 instead of 2 mL.

Comparative Example 2

Example 3 is repeated, however the 35 pellets employed are not treated with a dust suppressant. TABLE 1 Dust measurement and pellet surface observation of iron ore pellets treated with foamed oils. Fine material Adhered oil [%(w fine [%(w oil/w material/w Pellet surface Example pellet)] untumbled pellet)] observation Comparative 0 5.72 Red surface example 2 Example 3 0.22 1.54 Gray surface Example 3 0.26 1.10 Gray surface Example 3 0.29 0.77 Gray surface Example 4 0.29 1.4 Gray surface Example 4 0.30 1.71 Gray surface Example 4 0.31 1.56 Gray surface Example 4 0.37 1.47 Gray surface Example 4 0.46 1.27 Gray surface Example 4 0.49 1.47 Gray surface Example 4 0.58 0.90 Gray surface Example 4 1.04 0.91 Gray surface

The results show that oils can be successfully applied as a foam to reduce dust generation and surface oxidation of iron ore pellets. Soyabean oil was more effective than paraffin oil at equivalent dosages. 

1. Composition consisting essentially of a mineral substrate and a dust suppressant, which is adhered to the surface of the mineral substrate, wherein the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides.
 2. Composition according to claim 1, wherein the dust suppressant is a natural triglyceride or a mixture comprising natural triglycerides.
 3. Composition according to claim 1, wherein the mineral substrate is an ore pellet.
 4. Composition according to claim 1, wherein the mineral substrate is an iron-ore pellet.
 5. Composition according to claim 1, wherein the amount of dust suppressant is chosen in the range of from 0.05 to 2.5% by weight per weight pellet.
 6. Composition according to claim 1, wherein the dust suppressant is adhered to at least 80% of the surface of the mineral substrate.
 7. Method of reducing dust generation of mineral substrate comprising applying a dust suppressant to the surface of a mineral substrate having a temperature in the range of from 150 to 250° C. and an amount in a range of 0.05 to 2.5% by weight per weight of mineral substrate, wherein the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides.
 8. (canceled)
 9. Method of reducing dust generation of mineral substrate comprising applying a dust suppressant to the surface of a mineral substrate having a temperature in the range of from 100 to 250° C. and an amount in a range of 0.05 to 2.5% by weight per weight of mineral substrate, wherein the dust suppressant is applied in the form of a nonaqueous foam.
 10. Method according to claim 9, wherein the dust suppressant is applied in the presence of a surfactant.
 11. Method according to claim 9 wherein the dust suppressant is a natural or synthetic triglyceride or a mixture comprising triglycerides.
 12. Method according to claim 9, wherein the mineral substrate is an ore pellet.
 13. Method according to claim 12, wherein the ore pellet is an iron-ore pellet.
 14. Dust suppressant in the form of a nonaqueous foam. 